The present invention relates to the general field of manufacturing composite structures particularly utilized for the epitaxy of materials from the III/N group such as GaN, AlGaN, InGaN or materials from the III/V group such as GaAs or materials from the IV group such as germanium. The fields of application of the invention are electronics, optics and optoelectronics.
More precisely, the invention relates to a method of fracturing a composite structure along an embrittlement plane defined between two layers, the method comprising producing a fracture in the structure along the embrittlement plane.
Composite structures may be manufactured according to SMART CUT® technology. This technology allows a composite structure to be made by transferring a thin layer onto a support substrate.
One example of implementation of SMART CUT® technology applied to making SOI wafers is particularly described in document U.S. Pat. No. 5,374,564 or in the article by A. J. Auberton-Hervé et al. entitled “Why can SMART CUT change the future of microelectronics?,” Int. Journal of High Speed Electronics and Systems, Vol. 10, No 1, 2000, p. 131-146.
In general, SMART CUT® technology consists of implanting ionic species under a face of the donor substrate to form an embrittlement plane, to put the face of the donor substrate subjected to implantation in close contact with a support substrate, to perform a stabilization heat treatment for bonding, and to perform fracturing of the structure thus obtained at the level of the embrittlement plane to transfer the part of the structure between the surface subjected to implantation and the embrittlement plane onto the support substrate. Fracturing the structure may be done by thermal annealing at a given temperature and/or by supplying mechanical energy. The layer from the donor substrate defined between the embrittlement plane and the face that has undergone implantation is thus transplanted onto the support substrate.
The remaining layer of the donor substrate, called the “negative,” is recycled after its surface is polished and cleaned to be used again as a donor substrate in a new thin layer transfer.
The donor substrate requires special fabrication to present a low defect density. Therefore, the donor substrate is particularly costly. Thus, recycling the negative is particularly important to reduce manufacturing costs.
Such being the case, during the utilization of donor substrates in a hard and brittle material (such as GaN, SiC) or in a very fragile material (such as germanium or silicon), fracturing structures disposed horizontally or vertically may lead to breakage of 80% of the negatives. At the time of fracturing, the energy released, which may be very strong locally, may in fact cause the negatives to break.
Various solutions exist to improve the transfer of a thin layer by fracturing a substrate.
One of these known solutions is described in PCT application WO 2006/093817. It provides for reducing the formation of defects (bubbling, cracks and fractures) that appear in the transferred layer when the fracture energy is applied. For this purpose, this document proposes fixation of a substrate by a bonding method, forming a stiffener on the rear face of the support or donor substrate.
Another solution that is known and described in U.S. Pat. No. 6,858,517 applies more particularly to the transfer of a thin layer from an embrittled donor substrate onto a support substrate whose thermal expansion coefficient is different from that of the donor substrate. To reduce the risks of breakage of the transferred layer, this document provides for bonding a substrate, forming a stiffener on the support or donor substrate, the substrate stiffener having a thermal expansion coefficient close to that of the substrate onto which it is bonded.
Yet another known solution is described in U.S. Pat. No. 6,884,697. This solution aims to obtain a homogeneous roughness over the entire surface of the layers obtained. To do this, the embrittled donor substrate is placed horizontally in the furnace allowing fracture thermal annealing, and gripping means are provided to handle the layers horizontally in order to prevent any movement of one layer on another that may result in scratches being formed.
Although these solutions are satisfactory for improving the transfer of the thin layer by fracturing, they do not reduce the risks of breakage of the remaining layer of the donor substrate (i.e., the negative) obtained during fracturing. Thus, further improvements in this area are needed.